ZIP 2.0, the enhanced Zip Code Insulation Program, determines economic levels of thermal insulation for new and existing houses in any location in the United States, given the first three digits of its Zip code. Economic insulation levels are calculated for attics, cathedral ceilings, exterior walls, floors over unheated areas, slab floors, basement and crawlspace walls, ductwork in unconditioned spaces (attics and crawlspaces), and water heaters. Local climate data and default insulation costs and energy prices are retrieved from data files on the ZIP disk. The user can enter site-specific insulation costs, energy prices, heating and cooling system types and approximate efficiencies, and other parameters to customize the calculations for a specific house. ZIP was developed at the National Institute of Standards and Technology, under the sponsorship of the U.S. Department of Energy. ZIP and its supporting data files are provided on diskette for use with microcomputers having an MS-DOS operating system (typical IBM-PC/XT/AT and compatible systems).